A light waveguide is a solid body that transmits light such as a laser beam therethrough while confining the light beam to a specific region of the solid body. An optical fiber is an example of a light waveguide, wherein the light is confined to a long, narrow channel. In other applications, a planar light waveguide is required, wherein the light beam is confined to a planar region within the waveguide.
A planar light waveguide is normally fabricated by bonding a sheet of a core material to a piece of a first outer layer. The surfaces that are bonded together must be of optical quality. The core is next precisely thinned to a desired thickness dimension, typically in the tens-of-micrometers-thickness range. This bonding-and-thinning approach is required because the core cannot be initially furnished in the very thin dimension required prior to bonding to the first outer layer. During the thinning, the thinned surface must be maintained perfectly parallel to the side of the core bonded to the first outer layer, and the exposed surface of the core must have an optical-quality finish at completion. A second outer layer having a surface with an optical-quality finish is then bonded to the opposite side of the thinned-core from the first outer layer to complete the structure. Light is transmitted through the core in the final structure, which serves as a waveguide.
This conventional approach is difficult and expensive to implement. Contamination of the components is a concern during the multiple thinning, polishing, and bonding steps. The requirements for the several optical-quality surfaces and the precise, parallel thinning of the core to a small thickness dimension are difficult to accomplish in any event. They are prohibitive where the lateral extent of the core is tens of centimeters in either planar dimension. Current technology used with this fabrication procedure simply cannot fabricate such a structure with dimensional tolerances of the core on the order of a few micrometers, to produce a core on the order of a few tens of micrometers thick with the required degree of parallelism, over such large areas.
There is a need for an improved approach to fabricating planar waveguides that have the required core thickness and tolerances, particularly in large lateral sizes. The present invention fulfills this need, and further provides related advantages.